The present invention relates to a method for calibrating a trabecular index with a sawtooth-shaped rack that corrects an error in the trabecular index due to the characteristics of the image input device or radiographic conditions of an x-ray image when a bone mineral density is measured by setting up the trabecular index with trabecular patterns of a simple x-ray image.
Osteoporosis is a wide spread medical condition that affects the middle-aged and older populations. Especially, the condition is prevalent in postmenopausal women. Osteoporosis is characterized by an abnormal loss in bone mineral content, which leads to a tendency toward non-traumatic bone fractures and to structural deformations of bones. However, effective therapy for osteoporosis has not been developed yet. Only a few methods for reducing the possibility of occurrence of osteoporosis through physical exercise or appropriate diets are known. Accordingly, it is very important to develop a simple and inexpensive method of measuring bone mineral density so that osteoporosis can be diagnosed and treated in the early stages of the disease, thereby preventing further deterioration.
A bone mineral density measurement has been a basic tool for diagnosing osteoporosis because osteoporosis is characterized by an abnormal loss of bone mineral content. Various methods have been developed to obtain a quantitative measurement of bone mineral density. The most widely used method for measuring bone mineral density is dual photon absorptiometry with either an x-ray or nuclear source. The precision of this method to measure bone mineral density is within a few percent.
Two other methods for quantitatively measuring bone mineral density are Computerized Tomography and a Magnetic Resonance Imaging which provide three-dimensional bone density assessment, and separate estimations of cortical and trabecular bone densities. However, the routine use of these densitometries is precluded by their high costs.
Mechanical strength of the whole bone is determined mainly by the dense cortical bone. However, many recent studies have indicated that the trabecular bone is also an important factor in determining mechanical strength of bone. Moreover, it is well known that the trabecular bone is absorbed more rapidly than cortical bone in the case of osteoporosis. This implies that the trabecular bone is more reflective of the stage of osteoporosis and that early stage intervention in osteoporosis is possible through an evaluation of changes in the trabecular bone.
In this sense, many investigators have studied the trabecular patterns appearing on conventional x-ray images. The Saville index and the Singh index are available as clinical tools for assessing changes in trabecular patterns of x-ray images. These indices assess the stage of osteoporosis using density, direction, etc. of trabecular patterns appearing on x-ray images of the lateral lumber spine and the upper part of the femur.
Computerized image processing applies various textural methods to quantify changes in trabecular patterns appearing on an x-ray image, such as gray level statistics, frequency domain analysis, and fractal dimension analysis. These methods are reported to be somewhat successful to predict the fracture risk of bone.
Recently, a new method of trabecular indexing has been developed to quantify the trabecular pattern changes appearing on a simple x-ray image. This trabecular index method analyzes trabecular patterns appearing on an x-ray image and uses the analysis for the measurement of bone mineral density of the corresponding bone.
Unfortunately, when a trabecular index method is applied to a real x-ray image, the trabecular index of the corresponding bone may vary in accordance with the characteristics of an x-ray film digitizer and the x-ray radiographic conditions.
In general, each hospital uses different x-ray radiographic conditions and ray film digitizers. Thus, when the above trabecular indexing method is used by respective hospitals, the effect due to the difference of x-ray radiographic conditions and x-ray film digitizers should be corrected.
Accordingly, the present invention is directed to a method for calibrating a trabecular index with a sawtooth-shaped rack that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
The object of the present invention is to provide a method for calibrating a trabecular index with a sawtooth-shaped rack that corrects an error in a trabecular index due to the characteristics of an image input device or radiographic conditions of an x-ray image when a bone mineral density is measured by setting up a trabecular index with the trabecular patterns of a simple x-ray image.
Another object of the present invention is to provide a recording means for storing a program to realize a method for correcting a trabecular index.
Additional features and advantages of the invention will be set forth in the description that follows and in part will be apparent from the description, or may be learned by practicing the invention. The objectives and other advantages of the invention will be realized and attained by the structure pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages in accordance with the purpose of the present invention, as embodied and broadly described, the present invention includes a method for calibrating a trabecular index with a sawtooth-shaped rack, wherein bone mineral density is measured with a trabecular index. This index is calculated from an x-ray image and an error in the trabecular index is calibrated by a method including the following steps. The first step is preparing an x-ray image by radiographing a bone and a sawtooth-shaped rack together. The second step is attaining trabecular indexes from the x-ray image of the rack and the bone. The third step is calibrating the trabecular index of the bone with the trabecular index of the rack.
Preferably, the sawtooth-shaped rack consists of a thick sawtooth part modeling upon a thick trabecular bone and a thin sawtooth part modeling upon a thin trabecular bone.
More preferably, the sawteeth of the thick and thin sawtooth parts have the same pitch length and height, wherein the thickness under the sawteeth of the thick sawtooth part is thicker than a thickness under the sawteeth of the thin sawtooth part.
Furthermore, it is preferable that a calibrated trabecular index value xe2x80x9caaxe2x80x9d of the bone is attained by the following formula provided that a trabecular index value of the measured bone is xe2x80x9caxe2x80x9d, a trabecular index value of the thick sawtooth part is xe2x80x9cbxe2x80x9d, a trabecular index value of the thin sawtooth part is xe2x80x9ccxe2x80x9d, and the ideal reference trabecular index values of the two sawteeth are xe2x80x9cbbxe2x80x9d and xe2x80x9cccxe2x80x9d, respectively:
aa=(axe2x88x92c)(bbxe2x88x92cc)/(bxe2x88x92c)+cc
In another aspect, the present invention includes a recording means for storing a program for realizing a method of calibrating a trabecular index, the program includes the following steps. The first step is preparing an x-ray image by radiographing a bone and a sawtooth-shaped rack together. The second step is attaining trabecular indexes from the x-ray image of the rack and the bone. And the third step is calibrating the trabecular index of the bone with the trabecular index of the rack, wherein the program is read by the computer.
It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.